The advent of virtualization technologies for computing resources has provided benefits with respect to managing large-scale computing resources for many customers with diverse needs and has allowed various computing resources or computing services to be efficiently and securely shared by multiple customers. For example, virtualization technologies may allow a single physical computing machine to host multiple computing instances using a hypervisor. Each computing instance may be a guest machine acting as a distinct logical computing system on the physical computing machine (i.e., a physical host). Computing instances may be logically grouped into private groups where the computing instances communicate with each other and with external computing systems via a network that includes virtualized network devices.
A virtualized device may be software executed by a virtual machine (e.g., a computing instance) that performs the functions of a physical computing device. For example, a virtualized network device may perform the function of a physical network device, such as a network gateway, router, switch, firewall, NAT (Network Address Translation) device, etc. Virtualized network devices may lack some of the layer 2 (data link layer) capabilities specified in the OSI (Open Systems Interconnection) model for computer networks, making the detection of a functional state for an individual virtualized network device problematic as compared to methods that may be used to detect the failure of a physical network device.